Forwarding Inter-Switch Connection (isc) Frames in a Network-To-Network Interconnect Topology

1. A first network switch, comprising: a first network switch element coupled to a physical switch link to transmit a first untagged and not encapsulated frame for a local network over a first logical connection of the physical switch link to a first network switch element of a second network switch coupled to the physical switch link, when the physical switch link is part of an active topology of the local network; and a second network switch element coupled to the physical switch link to transmit a second untagged and not encapsulated frame for a foreign network over a second logical connection of the physical switch link to a second network switch element of the second network switch coupled to the physical switch link, when the physical switch link is not part of the active topology of the local network, and further to check a Media Access Control address and/or Service Identifier or Virtual Local Area Network Identifier (MAC-SA/VID) of a broadcast frame for a foreign network, and transmit the broadcast frame, or not, on the basis of such.

2. The first network switch of claim 1 , wherein when the physical switch link is not part of the active topology of the local network, the first network switch element is aware that the physical link is blocked according to a loop prevention protocol.

3. The first network switch of claim 1 , wherein the first network switch element and the second network switch element transmit their respective untagged and not encapsulated frames at different and nonoverlapping times.

4. The first network switch of claim 1 , wherein the first network switch element of the first network switch is a node in the local network and wherein the second network switch element of the first network switch is a node in the foreign network.

5. The network switch of claim 1 , wherein the second switch element is coupled to a third network via one of: a Network-to-Network Interface (NNI) connection; or a Multi-system Link Aggregation (MLAG) connection.

6. A first network switch comprising: a first network switch element coupled to a physical switch link to transmit a first untagged and not encapsulated frame for a local network over a first logical connection of the physical switch link to a first network switch element of a second network switch coupled to the physical switch link, when the physical switch link is part of an active topology of the local network; and a second network switch element coupled to the physical switch link to transmit a second untagged and not encapsulated frame for a foreign network over a second logical connection of the physical switch link to a second network switch element of the second network switch coupled to the physical switch link, when the physical switch link is not part of the active topology of the local network, the second network switch element further coupled to a third network via a Network-to-Network Interface (NNI) connection; and wherein the first network switch and the second network switch reside within the local network and wherein the third network switch accessible via the Network-to-Network Interface connection resides within the foreign network, wherein the foreign network is operated independently from the local network under different network management and administration, and wherein the Network-to-Network Interface connection forms a communication path between the local network and the foreign network.